Vehicular rack and pinion steering gears include an elongated flat gear or rack having teeth which mesh with mating teeth of a rotating pinion gear. The pinion gear is rotatably mounted on a steering shaft. As a steering angle is imparted to the steering shaft via rotation of a steering wheel, the pinion gear translates via engagement with the rack teeth, which in turn moves the rack in a corresponding steering direction. Tie rods are disposed at the distal ends of the rack. The tie rods are connected to front road wheels of a vehicle via a corresponding steering arm. Therefore, rack and pinion steering gears effectively convert rotational motion with respect to a steering axis into linear motion with respect to the rack while also providing a suitable level of gear reduction.
The steering functionality provided by typical rack and pinion steering gears may be electrically assisted in some designs. For instance, an electric steering motor may impart a steering torque overlay along the steering axis, e.g., in a column electric power steering (EPS) system or a pinion EPS system, while in other designs such as a rack EPS system the electric steering motor delivers torque assist to a particular part of the rack via a suitable drive mechanism. In an example of the latter design, a rotor axis of a steering assist motor is positioned parallel to a longitudinal axis of the rack. A belt, chain, gear set, or pulley system may be used to transfer torque from the off-axis steering assist motor to a ball screw device, and ultimately to the rack itself. Due to close manufacturing tolerances, transient impingement may occur in the various gears or torque transfer mechanisms of the steering system, with such impingement possibly resulting in a stick-slip or “stiction” condition that can affect overall steering precision and feel. The transient and largely unpredictable nature of such a stiction condition can complicate problem isolation, diagnosis, and correction.